The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Hybrid powertrains typically include an internal combustion engine (ICE), an electric motor (EM), and one or more torque generators that provide torque to a driveline to propel a vehicle. Two types of hybrid powertrains include a full hybrid powertrain and a mild hybrid powertrain. In a full hybrid powertrain, the EM drives the drivetrain directly, without transferring torque through a component of the ICE. In a mild hybrid configuration the EM is coupled to the ICE through an accessory drive. Torque generated by the EM is transferred to the drivetrain through the ICE. An exemplary mild hybrid powertrain includes a so-called belt alternator starter (BAS) system. In the BAS system, the EM is coupled to the ICE via a belt and pulley configuration, which drives other accessory components, such as pumps and compressors.
Powertrain torque control typically includes two torque control domains: axle torque and propulsion torque. In a mild hybrid powertrain, the propulsion torque is the output torque at the crankshaft of the ICE, which includes the EM torque contribution.
During an auto start of the engine, a control module spins up the engine using the electric motor. A crankshaft of the engine is rotated at higher speeds during auto start than during a conventional startup of an engine via a starter. Since fuel is not initially enabled during an auto start, compression and expansion pulses of the engine cause the spin-up of the engine to include increases and decreases in a rate of change of the engine speed.